I've been playing v 1.6 for a while now, my thoughts:
1) Does NOT overwrite v 1.5
2) If anything, its faster for me ( both fps and ping )
3) I like the new weapons ( especially t's )
4) Smoke grenade is now useful
5) ALT+TAB out without losing sound
6) New console "smart" console (i.e. you type cl_ and get a list of possible variables to change that match that string )
7) Auto-join server option if your desired server is full.
Never crashes on me or is "buggy". Don't know what the problem is for everyone else.